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Principles of Ecology Section ●2 Flow of Energy in an Ecosystem

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Principles of Ecology Section ●2 Flow of Energy in an Ecosystem chapter 2 Principles of Ecology section ●2 Flow of Energy in an Ecosystem -!). )DEA Before You Read Autotrophs capture energy, making it available for all If a pet had to survive without your care, how would its diet members of a food web. change? Write your ideas on the lines below. Read about how What You’ll Learn organisms get food and energy in their environment. ■ the fl ow of energy through an ecosystem ■ food chains, food webs, and pyramid models 3TUDY#OACH Read to Learn Make Flash Cards Make a fl ash card for each question Energy in an Ecosystem heading in this section. On the One way to study the interactions within an ecosystem is to back of the fl ash card, write the trace how energy fl ows through the system. All organisms are answer to the question. Use the classifi ed by the way they obtain energy. fl ash cards to review what you have learned. How do autotrophs obtain energy? All green plants and other organisms that produce their own food are the primary producers of food in an ecosystem. They are called autotrophs. An autotroph (AW tuh trohf) is an organism that captures energy from sunlight or inorganic substances to produce food. Autotrophs make energy available for all other organisms in the ecosystem. How do heterotrophs differ from autotrophs? A heterotroph (HE tuh roh trohf), also called a consumer, is an organism that obtains energy by consuming other organisms. A heterotroph that consumes only plants is an herbivore (HUR buh vor). Cows, rabbits, and grasshoppers are herbivores. Inc. Companies, a division of The McGraw-Hill © Glencoe/McGraw-Hill, Copyright 1. Defi ne What type of Heterotrophs that prey on other heterotrophs are known as heterotroph consumes only plants for energy? carnivores (KAR nuh vorz). Wolves and lions are carnivores. Omnivores (AHM nih vorz) eat both plants and animals. Bears, humans, and mockingbirds are examples of omnivores. 16 Chapter 2 Principles of Ecology Reading Essentials 011-022_Bio_SRE_C02_896099.indd 16 PDF Pass 3/4/10 10:04:15 AM How do detritivores help an ecosystem? Detritivores (duh TRYD uh vorz) decompose organic materials in an ecosystem and return the nutrients to the soil, air, and water. The nutrients then become available for use by other organisms. Hyenas and vultures are detritivores. They feed on animals that have died. Fungi and bacteria are also detritivores. Detritivores play an important role in the biosphere. Without them, the biosphere would be littered with dead organisms. The nutrients in these dead organisms would not be available to other organisms. Detritivores make these nutrients available for use by other organisms. 2. Explain How do Models of Energy Flow organisms in an ecosystem Ecologists study feeding relationships to learn how energy depend on detritivores? fl ows in an ecosystem. Ecologists use food chains and food webs to describe the fl ow of energy. Each step in a food chain or food web is called a trophic (TROH fi hk) level. Autotrophs are the fi rst trophic level in all ecosystems. Heterotrophs make up the remaining levels. Organisms at the fi rst trophic level produce their own food. Organisms at all other levels get energy from the trophic level before it. What is a food chain? A food chain is a simple model that shows how energy fl ows through an ecosystem. A typical grassland food chain is shown in the fi gure below. Each organism gets energy from the organism it eats. The fl ow of energy is always one way—into the consumer. An organism uses part of the energy to build new cells and tissues. The remaining energy is released into the environment and is no longer available to these organisms. Picture This Producer Omnivore 3. Label Draw a circle around the autotroph. Draw a box around the Plant Mouse heterotrophs. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Companies, a division of The McGraw-Hill © Glencoe/McGraw-Hill, Copyright Herbivore Carnivore Grasshopper Snake Reading Essentials Chapter 2 Principles of Ecology 17 011-022_Bio_SRE_C02_896099.indd 17 PDF Pass 3/4/10 10:04:18 AM What does a food web show? Feeding relationships are usually more complex than a 4. Synthesize Why might single food chain model can show. Most organisms feed on an ecologist use a food more than one species. A food web is a model that shows chain for one study and all the possible feeding relationships in an ecosystem. Food a food web for another study? webs give a more accurate picture of how energy fl ows in an ecosystem than food chains. What do ecologists model with an ecological pyramid? Ecologists also use ecological pyramids to model how energy fl ows through ecosystems. A pyramid model can be used to show energy fl ow in three different ways. Each level of the pyramid represents a trophic level. A pyramid of energy indicates the amount of energy available to each trophic level. In the energy pyramid below, notice that about 90 percent of the available energy is used by the organisms at each level. Some of the energy is used to build cells and tissues. Some is released into the environment as heat. Only about 10 percent is available to the next level of the pyramid. The biomass, or total mass of living matter at each trophic level, can also be modeled by an ecological pyramid. In a pyramid of biomass, each level shows the amount of biomass consumed by the level above it. A pyramid of numbers shows the number of organisms consumed at each trophic level in an ecosystem. The number decreases at each level because less energy is available to support organisms. GM Picture This 4HIRD LEVEL 4HIRD LEVEL 5. Explain How is mass CONSUMERS CONSUMERS measured on the pyramid !VAILABLEENERGYDECREASES !VAILABLEBIOMASSDECREASES %NERGYLOST GM of biomass? ASHEAT 3ECONDARY 3ECONDARY CONSUMERS CONSUMERS GM 0RIMARY 0RIMARY CONSUMERS CONSUMERS GM 0RIMARY 0RIMARY 0ARASITESANDDECOMPOSERSPRODUCERS PRODUCERS FEEDATEACHLEVEL Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Companies, a division of The McGraw-Hill © Glencoe/McGraw-Hill, Copyright 0YRAMIDOF%NERGY 0YRAMIDOF"IOMASS 18 Chapter 2 Principles of Ecology Reading Essentials 011-022_Bio_SRE_C02_896099.indd 18 PDF Pass 3/4/10 12:03:38 PM.
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